The present disclosure relates to a method for damping torsional oscillations in a drive train component, in particular a power production plant, and to a computing unit for the implementation thereof.
Drive trains, comprising components such as gearboxes, clutches and connecting elements (shafts), are important constituent parts, amongst others, of various electrical power production plants, such as wind power plants, water power plants, etc. The drive train fulfills the task of producing a mechanical connection between a drive (for example a rotor of a wind power plant) and an output (for example an appropriate generator), via which energy is transmitted via a rotational movement. Drive train components, such as gearboxes, are used to transform the rotational speed and the torque which are present on the drive into values which correspond to the working range of the generator. Clutches are used as required for separation between drive and output, and shafts produce the mechanical connection between the components involved. In addition, further components, such as mechanical brakes or the like, can be integrated in the drive train.
Since the components involved cannot be fabricated as rigidly as desired but have a finite rigidity, they can be excited into natural oscillations. Such an excitation can be carried out, for example, by a non-constant input power (in the case of wind power plants, for example as a result of gusts or wind turbulence), by external interference or by inherent movements of other plant components. In addition, oscillations of another origin can result in oscillations in the drive train; in the case of a wind power plant, for example, tower oscillations or oscillations on account of the tooth engagements of a gearbox.
Oscillations have a detrimental effect on the service life of the components involved, in particular the gearbox. Continuous threshold loads increase the wear of the affected components and lead to shorter replacement intervals, which represents a financial and technical burden on the plant and network operator and reduces the plant income. In particular from the point of view of the expected increase in the wide spread of wind power plants in the offshore sector in the foreseeable future, this aspect plays an ever greater role, since the replacement of damaged components is made more difficult there. The result is therefore the objective of reducing these oscillations in order to increase the service life of the components.
In order to avoid oscillations, use can be made of generators, the load of which is adjustable. The generator can be, for example, a double-fed asynchronous generator, which on the stator side is connected directly to the network and on the generator rotor side is supplied via an intermediate DC circuit, by which means voltages and currents of different frequency and amplitude can be impressed on the generator rotor. In addition, synchronous generators which are connected to the network via inverters with intermediate DC circuit and are accordingly adjustable are used in the prior art. By means of the aforementioned actuating possibilities, the generator can be predefined a moment which is matched to the damaging oscillations, by which means it reduces the latter and appropriately damps the torsional moment present in the drive train.
For instance, a method is known from DE 10 2007 019 907 B4 which, by using the generator rotational speed, forms a control difference via a retardation element that is capable of oscillation, from which a corrective moment for generator control is determined.
A similar approach is followed in US 2008/0067815, according to which a signal is generated from changes in the generator rotational speed, by means of which damping is implemented via the generator actuating torque.
It is to be viewed as disadvantageous in these solutions that the damaging oscillations of the torsional moment are determined with only restricted accuracy and, accordingly, the quality of the compensating operations is also limited. In particular, the determination of the oscillations from the rotational speed is afflicted with considerable inaccuracies.
DE 10 2009 059 669 A1 describes determining and damping the torsional moment prevailing in the drive train from an angular difference between rotor and generator position. For this purpose, however, the rigidity of the drive train must be known very accurately.
It is therefore desirable to damp torsional oscillations in a drive train component as simply and effectively as possible.